Kinetic modeling of sulfonamide degradation by UV/H2O2: Deduction of ROH,UV modeling and application.

Eight sulfonamide (SA) antibiotics were effectively degraded using a UV/H2O2 process in a quasi-collimated beam apparatus, utilizing optimized fluence quantification. Fluence-based rate constants (kk'SA) for the UV/H2O2 process were established. A curve-fitting method, derived from ROH,UV modeling, was developed for the UV/H2O2 process to quantitatively assess the impact of critical factors, including water quality and direct UV photolysis. It was observed that k'SA values approached a limiting value as initial H2O2 concentration increased. The specific second-order rate constants for •OH reactions with neutral and anionic SA species were determined to be within (2.2-5.7) × 10⁹ M⁻1 s⁻1, showing minimal variation among species. For the eight SAs studied, k'SA values were calculated from 3.9 × 10⁻⁴ to 6.0 × 10⁻2 cm2 mJ⁻1 across a typical pH range of 6.5-9.5. Direct UV photolysis was notably significant in SA degradation, particularly for sulfisoxazole, contributing at least 35%. An energy cost equation was formulated to evaluate the cost-effectiveness of SA degradation by UV/H2O2 and optimize operational parameters. This model, validated in real water scenarios, shows promise for predicting SA removal in UV/H2O2 processes. The developed curve-fitting method, pH-independent and accounting for both direct photolysis and OH radical reactions, is apt for modeling mixed-contaminant degradation in UV/H2O2 processes, simplifying calculations in ROH,UV modeling.